A submarine optical communications cable is an optical cable suitable for being laid beneath the sea, for implementing a point-to-point optical link supporting exchange of information between two endpoints located ashore.
The point-to-point optical link may be either repeatered or unrepeatered. In the first case, the submarine optical communications cable forming the link merely carries light signals. In the second case, the submarine optical communications cable forming the link carries both light signals and electrical power for supplying the submarine repeaters of the link.
In both cases, construction of a submarine optical communications cable typically comprises an optical core containing optical fibers within an inner tube—generally made of stainless steel, aluminium or polymeric material—surrounded by one or more layer(s) of metal wires encircled, in turn, by an outer aluminium layer. The metal layers protect the optical core against the detrimental effects inherent to installation beneath the sea (especially in deep water), such as for instance moisture penetration and mechanical stresses (in particular, hydrostatic pressure). The one or more layer(s) of wires (typically steel wires) are mainly responsible for the mechanical properties (in particular, the hydrostatic pressure resistance) of the cable.
GB 2101505 discloses a method for manufacturing an optical fiber cable for submarine use, whose optical fiber cable core comprises a plurality of optical fibers held together around a strength member by a preform, and an aluminium tube in which the preform is arranged. A layer of high tensile steel wires are stranded helically over the tube, thereby forming a stranded strength member. An oversize aluminium tube is then directly extruded coaxially over the stranded strength member by a continuous extrusion process. The tube is subsequently drawn down and swung onto the stranded strength member so that the tube material fills at least the interstitial spaces between the wires and is in intimate contact with the layer of stranded wires.
U.S. Pat. No. 4,156,104 discloses a repeatered submarine cable where the cable core is surrounded by an outer strength member formed by a plurality of stranded steel wires which are successively wrapped in superimposed layers around the outer diameter of the core. A non-porous conductive jacket of aluminium or copper is then formed directly over the outer layer of stranded wires. The jacket surrounding the steel wires forms a DC conducting path for powering optical repeaters spaced at intervals along the cable, and also serves as a moisture barrier for the optical transmission lines disposed in the cable.
EP 0 092 980 discloses an overhead earth conductor comprising a central core of aluminium formed from a single extrudate of substantially C-shaped transverse cross-section whose limbs have been folded inwardly so that the gap between the free ends of the limbs is closed and the central core is of substantially circular cross-section. Extending through the length of the central core is an elongated compartment in which is loosely housed an optical fiber. A layer of galvanized steel wires surrounds the central core, the wires being helically laid around the central core. A circumferentially continuous outer layer of aluminium surrounds the layer of galvanized steel wires, the outer layer being formed from a single extrudate of substantially C-shaped transverse cross-section whose limbs have been folded inwardly so that the gap between the free ends of the limbs is closed. Aluminium of the central core and aluminium of the outer layer partially fills the interstices between the steel wires. Spaces of the interstices between the galvanized steel wires not occupied by aluminium are substantially filled with water-impermeable grease.